The present invention relates to imaging devices, and more particularly, to methods imaging devices capable of detecting flicker.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of complementary metal-oxide semiconductor (CMOS) image sensors which includes individual CMOS image pixels arranged in rows and columns. Imaging devices often use a rolling shutter scheme in which the image pixels reset on a row-by-row basis (i.e., each row of image pixels captures image data a different times).
Imaging devices can be operated outdoors and indoors. Indoor light sources are commonly powered by an alternating current (AC) power supply cycling at a frequency of 50 Hz or 60 Hz. As a result, light sources powered using an AC power supply may exhibit a flicker at a flicker frequency (FF) that is double the AC frequency of the power source, i.e., 100 Hz or 120 Hz.
A rolling-shutter-based imaging device may therefore generate a captured image having bright and dark portions because of fluctuations in the light source (i.e., the captured image is said to exhibit flicker). In cases where multiple images are obtained and displayed, such as in a video device or a continuous digital camera finder display, flicker may be apparent. In conventional imaging systems, flicker is reduced by setting the integration time (sometimes called exposure time) of each pixel row to be a multiple of the flicker frequency. This method, however, requires prior knowledge of the flicker frequency.
It would be desirable to provide imaging devices capable of automatically detecting flicker and correcting the imaging process accordingly.